Process for the internal sizing of paper with a salt of a substituted succinic acid



V pulp with agitation;

United States Patent 3,139,373 THE INTERNAL SIZING F PROCESS FOR SUC- This invention relates to the manufacture of paper and more particularly, to a new and improved method of paper sizing.

Current procedures for paper sizing involve two distinct principal methods: (1) internal sizing wherein the sizing agent is mixed with the fiber furnish and thereafter the entire mass is formed into a sheet having a uniform distribution of fibers and sizing agent, and (2) surface sizing which involves the application of a sizing agent to the surface of an already formed paper. This invention is particularly concerned with the internal sizing procedure.

Rosin size, which consists mainly of a body of abietic acid, is currently the most widely employed sizing agent for the internal sizing of paper. An aqueous solution of the sodium salt of this body, obtained by dissolving rosin in a solution of an alkali, customarily is added to paper and, by treatment with a soluble aluminum salt, the rosin size is precipitated and deposited upon the fibers. Although rosin size is currently the most Widely used type of paper size, it nevertheless possesses certain undesirable characteristics. More specifically, rosin size in the paper tends to lower the brightness of the paper as well as the burst, tensile, tearing and folding strengths. Furthermore, paper which has been sized with a rosin size tends to lose strength on aging. More recently, ketene dimers have been suggested as sizing agents. These ketene dimers are added to the paper pulp to convert the hydroxyl groups of the fibers to hydrophobic groups which repel water. Although the use of ketene dimers as paper sizing agents in the internal sizing procedure reduces some of the undesirable characteristics of rosin sizing, unfortunately new problems are created. For example, paper sizing with ketene dimers is inefifective in the presence of alum and therefore presents a serious deterrent to its use since most paper-mill systems in operation today contain alum. Furthermore, sizing cannot be obtained with ketene dimers on reworked papers since the majority of these reworked papers contain residual alum from prior sizing processes. A further disadvantage of ketene dimer sizing is that the retention of the ketene dimer is poor Whenit is added at the wet end of the process, and consequently, costly additives must be employed to increase the retention of the ketene dimer size by the fibers.

An object of the present invention is to provide an eiiicient economical method for the internal sizing of paper. Another object of the invention is to provide new sizing agents for internal sizing of paper. A further object of the invention is to provide an improved paper product. Other objects and advantages will become apparent from the following description.

In accordance with the present invention, internal sizing of paper is effected by dispersing a saponified substituted succinic anhydride or its corresponding acid having a hydrocarbon radical of 8 to 15 carbon atoms, inclusive,

in an aqueous slurry of paper pulp and adding a precipitating agent to convert the saponified substituted succinic anhydride or acid to an insoluble form which is deposited on the fibers of the pulp. The treated pulp may then be formed into sheets or webs in the conventional manner.

The new sizing agents of the present invention employ 3,139,373 Patented v June 30, 1964 substituted succinic anhydrides or its corresponding acids having the following formulas ice I RHC-b\ Hie-o b (I rt-nc 3-o-on HgC-(fi-OH O wherein R is a hydrocarbon radical which can be an alkyl,

alkene, alkyne or aryl alkyl group having 8 to 15 carbon atoms, inclusive, and preferably 10 to 14 carbon atoms.

and

' The preferred hydrocarbon radical is an alkene hydrocarbon wherein the double bond is adjacent the succinic anhydride group. Hydrocarbon radicals containing less than 8 carbon atoms or more than 15 carbon atoms were tried, but gave unsatisfactory results. Illustrative of compounds suitable for the present invention are n-octenylsuccinic anhydride and its isomers; nonenylsuccinic anhydride and its isomers; n-decenylsuccinic anhydride; dodecenylsuccinic anhydride and its isomers; n-tetradecenylsuccinic anhydride; n-octadecenylsuccinic anhydride; 3--

(ethylphenyl)butane-1,2-dicarboxylic acid anhydride; 3- methy1-3- (isopropylphenyl) -butane,1,2-dicarboxylic acid anhydride. Acids corresponding to the above anhydrides may also be employed.

The new sizing agents when used in the internal paper sizing procedure produce sized paper having superior qualities over rosin sized paper with regard to brightness, tensile strength, folding strength and retention of strength on aging of the sized paper; and surprisingly, these superior qualities are attained at appreciably lower concentrations of sizing agent than are required for rosin sizing. Effective sizing according to the invention has been accomplished with concentrations of 0. 5% and in some cases as low as 0.2% of the saponified substituted succinic compound, and the sizing eifects obtained with these amounts compare favorably, and in many cases are superior, to the effects obtained with rosin sizes at concentrations of 1 to 3 /2% based on the weight of the paper pulp. Another practical advantage of the present invention is that these new sizing agents can replace rosin sizes in whole or in part, since the process of the invention is compatible with equipment and procedures now in operation for rosin sizing.

Basically, internal sizing is accomplished by dispersing a water soluble metal salt of the substituted succinic acid,

. obtained by saponifying a substituted succinic anhydride,

or acid, e.g. an alkali metal salt of the substituted succinic acid, preferably the sodium salt, in an aqueous paper-pulp slurry and converting the saponified substituted succinic anhydride or acid to an insoluble form by treatment with a precipitating agent, i.e. a metal compound which reacts with the soluble saponified substituted succinic anhydride or acid to form an insoluble metal salt of the substituted succinic acid. Aluminum salts, particularly alum, have been found to be especially effective as the precipitating agents. The pulp, internally sized with the substituted succinic acid salt, is formed into a sheet in a manner conventional in the paper industry.

A convenient procedure is to dissolve the substituted succinic acid (or anhydride which converts to the acid) in an aqueous solution of an alkaline material such as sodium hydroxide to form the sodium salt of the substituted succinic acid and to add this aqueous solution of saponified substituted succinic acid, with sufficient agitation or stirring to insure thorough mixing, to the aqueous paper pulp slurry. Saponified substituted succinic anhydride is synonymous with salt of the substituted succinic acid since treatment of the anhydride with aqueous alkali (saponification) results in converting the anhydride to the salt of the acid. Thereafter, to the mixed slurry of paper pulp and saponified substituted succinic anhydride is added a precipitating agent, aluminum sulfate, which converts the saponified substituted succinic anhydride to the insoluble form which is deposited upon the fibers. An important property of the substituted succinic anhydride sizing agents of the present invention is their compatibility with alum which latter, because of its availability and low cost, is conventionally employed as a precipitating agent. In the manufacture of paper, the pulp frequently has a constituent reworked paper which contains residual alum and for this reason alone it is most important that the internal sizing agent be compatible with alum. Control of pH is an important factor in obtaining good sizing efiiciency. Although initial pH values of the paper slurry prior to the addition of the sizing and precipitating agent may vary considerably, and are usually from about 6 to 8, the final pH, i.e. the pH value after the addition of size and alum to the paper slurry, should be desirably in the range of 4.0 to 5.5 for maximum sizing efficiency. The final pH may be conveniently adjusted to within this range by the addition of alkaline or acid mediums such as dilute solutions of sodium carbonate or sulfuric acid.

In a preferred method, an alkenyl succinic anhydride having 10 to 14 carbon atoms in the alkenyl group, preferably dodecenylsuccinic anhydride, is saponified by mixing with sodium hydroxide, and heating until the dodecenylsuccinic anhydride is completely dissolved. A temperature of about 100 C. is suitable for this purpose. The sodium salt of dodecenylsuccinic acid which forms is then dissolved in water to form an aqueous solution, and this solution is added to the paper pulp slurr for example in the beater of a paper making system. This mixture is then agitated to thoroughly mix the two masses. Thereafter the saponified dodecenylsuccinic anhydride is set in the pulp fiber by the addition of about a chemical equivalent quantity of alum. The amount of alum employed generally depends on the amount of size, the character of the stock, and the pH of the pulp slurry. As an illustration, about 0.38% alum gives efficient sizing with 0.2% dodecenylsuccinic anhydride in pulp slurries with initial pH values of 6 to 8. Additional amounts of alum, up to 0.75%, may be added without producing any adverse effects. The final pH value of the slurry after addition of the sizing agent and alum should be in the range of 4.0 to 5.5 with optimum results being obtainable when the final pH value is about 4 to 5. Addition of controlled amounts of dilute sodium carbonate or sulfuric acid is an effective means of adjusting the pH value.

The amount of the dodecenylsuccinic anhydride applied to the pulp may be varied depending upon the requiremerits for the sized paper. Results superior to rosin sizing are obtained at concentrations of dodecenylsuccinic anhydride lower than required for similar sizing with rosin sizes. Comparative analysis has indicated that as low as 0.2% saponified dodecenylsuccinic anhydride based on bone dry pulp is as effective as 1% concentration of a superior grade of rosin size. With this concentration of the saponified dodecenylsuccinic anhydride, i.e. 0.2%, it was noted that the sized paper had better resistance to water penetration, and had better aging stability than could be achieved by rosin sizing. A feature of the present invention is'that the saponified dodecenylsuccinic anhydride is compatible with rosin sizing procedures and particularly good results are obtained with mixtures of saponified dodecenylsuccinic anhydride and rosin size where it is desired that the paper contain a moderate amount of size. The use of saponified dodecenylsuccinic anhydride in combination with rosin size results in a substantial decrease in the amount of rosin size required to produce sized paper of the same quality. Furthermore, this feature of the invention is particularly advantageous 41 since a gradual changeover from present rosin sizing procedures may be accomplished.

Generally the sizing efiiciency of the treated paper may be determined in a variety of ways. A particularly suitable procedure and one which has received considerable attention in the paper sizing industry is the Cobb size test, procedure T441 of the Technical Association of the Pulp and Paper Industry (TAPPI); In this procedure, an area of the sheet is defined by clamping it under a metal ring 10 cm. in inside diameter, and then the ring is filled with Water. After a measured interval of time, usually 1 to 5 minutes, the water is poured off, the ring is removed, and the paper is blotted to remove surface Water. The amount of water absorbed is determined from the weights of the paper before and after the exposure, and the Cobb size value is calculated and reported as grams of Water absorbed per square meter of paper. The lower the Cobb value, the better the sizing. For a 3 minute exposure time, a value of 50 g./m. or lower indicates good sizing.

The following examples illustrate the invention.

EXAMPLE '1 The following example shows the sizing eificiency of various substituted succinicanhydrides of the present invention.

Handsheets containing 0.5 sizing agent were prepared as follows:

A slurry for each substituted succinic anhydride to be tested was prepared by tearing into small pieces 4.0 grams of 60-brightness pulp which was then placed into a Waring Blendor with 400 ml. of distilled water. The mixture was agitated for 2 minutes and thereafter the required amount of solution of the sodium salt of the substituted succinic acid to give 0.5% based on the weight of the pulp was added and agitation was continued for an additional 1 minute. A solution of alum containing 0.6% alum based on the weight of the pulp was then added, followed by agitation for an additional 1 minute and the pH was adjusted in the range of 4 to 5.5. The action of the Waring Blendor was suflicient for complete disintegration of the pulp sheets and the attainment of a Canadian Standard freeness value of 750 for the pulp.

Handsheets were formed in a Williamson 8): 8" sheet mold with lSO-mesh stainless steel screen. For each handsheet, the slurry of the sized pulp was poured into the sheet mold; diluted to 5 liters; and the water was drained off to form a sheet. The sheet was removed from the screen on a blotter, pressed between blotters for 1 to 2 minutes at p.s.i., and then dried on an electric dryer at C. The sizing efficiency was determined by the Cobb size test according to TAPPI procedure T441, and the results are tabulated 1n Table I. a

Table I 0.5% size pH of size Compound solution Final Cobb pH size Nonenylsuccinic anhydride 10. 5 4. 3 31 3-(Ethylphenyl)butane-1,2-dicarboxylie acid anhydride 6. 8 4. 1 44 Oetenylsuoeinic anhydride isomer (from caprylene) 6. 3 4. 0 34 3-Methyl-3-(isopropylphenyl)butane- 1,2-d1carboxylic acid anhydride 6. 8 4. 3 33 Octenylsuccirnc anhydride isomer (from di-isobutylene) 6. 4 4. l 34 n-Octylsuceinic anhydride (from l-octene) 6.5 4.0 36 Nonenylsuecinic anhydride isomer (from tripropylene) 7. 4 4. 4 30 n-Decenylsuccinic anhydride (from 1- decene)... 6.9 4.0 32

Dodecenylsuccinie anhydride isomer (from butylene trimer) 7. 4 4. 0 33 Dodecenylsucciuic anhydride isomer (from propylene tetramer) 7.6 4. 2 33 n-Tetradecenyl-succinic anhydride (from l-tetradecene) 7.8 4. 0

The anhydride was mixed with the calculated equivalent quantity of sodium hydroxide; the solids concentration of the salt solution was 0.5%.

The pH value or the pulp slurry, after addition of size and alum. For 3 minute penetration time.

EXAMPLE 2 The following example shows the eifectiveness and uniformity of saponified dodecenylsuccinic anhydride as a paper size at a concentration of 0.2%.

One pound of sheeted, 60-brightness pulp was torn into small pieces and put into a Valley one-pound pulp beater with 22 liters of water. The pulp was dispersed by running the beater for a few minutes without any weight on the lever arm of the bed plate. Then a 5500 gram weight was hung on the lever arm of the beater and the pulp was lgeaten for 2 hours to a Canadian Standard freeness of A portion of the beaten-pulp slurry (3.9 liters) was diluted with water to make 12 liters. The pulp solids content of the dilute suspension was determined by vacuum filtering the pulp from 500 m1. of the suspension and then drying the pad of pulp to constant weight. The required amount of solution to give 0.2% saponified dodecenylsuccinic anhydride on the weight of pulp was then added to the suspension while the pulp was being stirred with a high speed mixer. The pulp was stirred for 30 minutes after the size was added, then a 1.0% solution of alum was added to give 0.6% alum on the Weight of pulp and the slurry was stirred for a few more minutes.

Ten 4-gram handsheets were formed according to the procedure of Example 1. The Cobb size measurements on handsheets prepared in this manner showed good agreement in values. The average Cobb size value for the 10 sheets was 23 with a maximum of 26 and a minimum of 18.

EXAMPLE 3.

Two sets of handsheets were prepared, one set containing concentrations of saponified dodecenylsuccinic anhydride of 1% and 0.2%, respectively, and the other set containing concentrations of rosin size of 2 /2%, 1% and 0.2%. The handsheets were prepared according to the procedure of Example 1 except that appropriate volumes of the solutions of the sodium salt of dodecenylsuccinic acid and of the rosin size as well as of the alum were used to provide the above concentrations based on the dry pulp.

The handsheets were then evaluated for sizing efficiency by the Cobb test method. The results are indicated below.

. Cobb size g.lm. at indicated size concentration Size Saponified dodecenylsuccinicanhydride. Rosin size EXAMPLE 4 The following example shows the effects of prolonged aging on sizing and on the strength of paper sized with saponified dodecenylsuccinic anhydride and compares saponified dodecenylsuccinic anhydride with rosin size. The paper specimens prepared according to Example 1 were heat aged according to TAPPI procedure T453- M48, by heating for 72 hours at 105 C. This accelerated aging is generally considered to be equivalent to about 25 years of normal aging. According to the information given with the TAPPI procedure, the property of the paper that is most affected by aging is the brittleness; therefore, the aged papers were evaluated by measurements of folding endurance. Cobb size measurements were also made on aged and unaged papers. Five measurements of Cobb size values and of folding endurance were made on each sample. The average results from the measurements on aged and unaged paper specimens are shown in the table below.

RESULTS FROM COBB SIZE AND FOLDING ENDURANCE MEASUREMENTS ON PAPER HANDSHEETS BEFORE AND AFTER AGING Cobb size (1 Folds to break min.) Size Percent Before After Before After aging aging in aging Dodeeenylsuccinic anhy- V (iride 0.2 25 20 64 45 Rosin size 1.0 24 20 16 27 2. 5 19 17 13 13 e The handsheets were heated 72 hours at C.

The aged and the unaged specimens were conditioned for 48 hours at 72 F. and 50% relative humidity before making measurements. Folding endurance was measured with strips of paper 1.5 cm. wide, according to TAPPI standard T4223m. An M.I.T. Folding Endurance Tester was used for the measurements.

EXAMPLE 5 The following example shows the effect of saponified dodecenylsuccinic anhydride when combined with rosin size.

Papers were prepared with varying amounts of saponified dedecenylsuccinic anhydride and rosin size to determine if the two sizes were compatible and what sizing properties this combination possessed.

The results of sizing measurements on the papers are given below and show that as little as 041% of the rosin size combined with0.l% of saponified dodecenylsuccinic anhydride gave an excellent sizing effect with a Cobb size value of 27. 1 RESULTS FROM COBB SIZE MEASUREMENTS ON PAPER a With 0.6% alum based on pulp. b For 1 minute penetration time.

EXAMPLE 6 As a check on the reproducibility of sizing with the mixed sizes, a large batch of pulp was prepared and sized with 0.1% saponified dodecenylsuccinic anhydride and 0.2% rosin size by the procedure described in Example 2. Alum (0.6%) was added to set the size, and 10 replicate handsheets were made. The average Cobb size value for the 10 handsheets was 20 and the range of values was from 19 to 24 which is considered to be excellent reproducibility.

Although certain preferred embodiments of the invention have been disclosed for purposes of illustration, it will be evident that various changes and modifications may be made therein without departing from the scope and spirit of the invention.

I claim:

1. In a process for the internal sizing of paper wherein an aqueous suspension of paper pulp is admixed with 7 a sizing agent and a precipitating agent to set the sizing agent on the fiber and the mass formed into a sheet, the improvement comprising incorporating as sizing agent a water soluble salt of a substituted succinic acid having the formula R-Ho-d -53 wherein R is a hydrocarbon radical selected from the group consisting of an alkyl, alkene, alkyne and aryl alkyl having 8 to 15, inclusive, carbon atoms.

2. A process as claimed in claim 1 wherein the water soluble salt of the substituted succinic acid is produced by saponifying the corresponding substituted succinic anhydride.

3. A process as claimed in claim 1 wherein the hydrocarbon radical contains 10 to 14, inclusive, carbon atoms.

4. In a process for the internal sizing of paper wherein an aqueous suspension of paper pulp is admixed with a sizing agent and. a precipitating agent to set the sizing agent on the fiber and the mass formed into a sheet, the improvement comprising incorporating as sizing agent a water soluble salt of a substituted succinic acid having the formula wherein R is an alkene hydrocarbon having 10 to 14, inclusive, carbon atoms with the double bond adjacent the succinic acid group.

5. A process for the internal sizing of paper which comprises incorporating the sodium salt of dodecenylsuccinic acid in an aqueous paper pulp slurry, adding aluminum sulfate to the slurry to convert the soluble sodium salt of dodecenylsuccinic acid to the insoluble form which deposits upon the fiber, adjusting the pH of said slurry to within the range of about 4.0 to 5.5, and forming the mass into a sheet.

6. A process for the internal sizing of paper which comprises incorporating the sodium salt of nonenylsuccinic acid in an aqueous paper pulp slurry, adding aluminum sulfate to the slurry to convert the soluble sodium salt of nonenylsuccinic acid to the insoluble form which deposits upon the fiber, adjusting the pH of said slurry to within the range of about 4.0 to 5.5, and forming the mass into a sheet.

7. A process for the. internal sizing of paper which comprises incorporating the sodium salt of 3-methyl-3- (isopropylphenyl)butane-1,2-dicarboxylic acid in an aqueous paper pulp slurry, adding aluminum sulfate to the slurry to convert the soluble sodium salt of B-methyl 3-(isopropyphenyl)butane-1,2-dicarboxylic acid to the insoluble form which deposits upon the fiber, adjusting the pH of said slurry to within the range of about 4.0 to 5.5, and forming the mass into a sheet.

8. A process for the internal sizing of paper which comprises incorporating the sodium salt of n-tetradecenyl succinic acid in an aqueous paper pulp slurry, adding aluminum sulfate to the slurry to convert the soluble sodium salt of n-tetradecenylsuccim'c acid to the insoluble form which deposits upon the fiber, adjusting the pH of wherein R is a hydrocarbon radical selected from the group consisting of an alkyl, alkene, alkyne and aryl alkyl having 8 to 15, inclusive, carbon atoms.

10. A process for the internal sizing of paper which comprises incorporating saponified rosin and a sodium salt of dodecenylsuccinic acid in an aqueous paper pulp slurry, adding aluminum sulfate to the slurry to convert the soluble sodium salt of dodecenylsuccinic acid to the insoluble form which deposits upon the fiber, adjusting the pH. of said slurry to within the range of about 4.0 to 5.5, and forming the mass into a sheet.

11. A sized paper comprising a fibrous cellulosic web which has been internally sized with a salt of a substituted succinic acid having the formula wherein R is a hydrocarbon radical selected from the group consisting of an alkyl, alkene, alkyne and aryl alkyl having 8 to 15, inclusive, carbon atoms.

12. A. sized paper comprising a fibrous cellulosic Web which has been internally sized with a salt of a substi:

tuted succinic acid having the formula wherein R is an alkene hydrocarbon having 10 to 14, inclusive, carbon atoms with the double bond adjacent the succinic anhydride group.

13. A sized paper comprising a fibrous cellulosic web which has been internally sized with a salt of dodecenylsuccinic acid.

' 14. A sized paper comprising a fibrous cellulosic web which has been internally sized with saponified rosin and saponified dodecenylsuccinic acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,996,707 Nathansohn Apr. 2, 1935 2,680,751 Prichard June 8, 1954 3,016,325 Pattiloch ,Jan. 2, 1962 3,022,321 Copenhaver Feb. 20, 1962 3,102,064 Wurzburg et a1. Aug. 27, 1963 FOREIGN PATENTS 804,504 Great Britain Nov. 19, 1958 

1. IN A PROCESS FOR THE INTERNAL SIZING OF PAPER WHEREIN AN AQUEOUS SUSPENSION OF PAPER PULP IS ADMIXED WITH A SIZING AGENT AND A PRECIPITATING AGENT TO SET THE SIZING AGENT ON THE FIBER AND THE MASS FORMED INTO A SHEET, THE IMPROVEMENT COMPRISING INCORPORATING AS SIZING AGENT A WATER SOLUBLE SALT OF A SUBSTITUTED SUCCINIC ACID HAVING THE FORMULA 